The present invention relates generally to electric resistance heaters, most typically heaters associated with catalytic converters, and more specifically to envelopes or enclosures containing electrically heatable catalytic converters and which have an electrode installed therein to preheat the catalyst contained within the converter envelope.
Catalytic converters are commonly employed commercially in the automotive industry for reducing internal combustion engine exhaust emissions such as nitrogen oxides, carbon monoxide, and various hydrocarbons. Typically, a catalyst contained within a catalytic converter does not effectively treat exhaust gases until the catalyst within the converter has been heated by the exhaust gases to a temperature in which the catalyst is able to become active. Thus, there is a period of time during the initial start-up of a cold engine when the exhaust gases are not being fully treated by the catalyst. This results in an increased quantity of undesired emissions being released to the atmosphere.
One tactic to reduce the quantity of undesired exhaust emissions during the cold engine start-up phase is to preheat the catalyst in order that the catalyst can be active during this phase. Electrically heating the catalyst with electric resistance heating units has proven to be a convenient and expedient method of preheating the catalyst prior to, and during, the cold engine start-up phase.
As a result of employing electric resistance heating units to preheat the catalyst in catalytic converters, there has developed a need to provide reliable electrode assemblies that lend themselves to being easily installed in the heater envelope without inducing exhaust gas leaks about the electrode. Achieving a reliable and simple electrode installation is complicated by the fact that these converters are rapidly and repeatedly heated to temperatures on the order of 1000.degree. C. in use. This involves significant thermal expansion and contraction as the units repeatedly cycle from low ambient temperatures to the relatively high operating temperatures associated with rapid catalytic oxidation. Of course, at electrode installation and throughout the life of the catalyst unit, the electrode installation arrangement must not allow the electrode to make electrical contact, or ground, with the heater envelope.
Thus, it can be appreciated that there is a need in the art to provide electrode assemblies, and methods of electrode installation, which will withstand the adverse conditions in which electric heaters for catalytic converters operate. It can also be appreciated that such electrode assemblies must not be unduly complex, and that the method of electrode installation be easily and readily carried out on an assembly line with minimal added converter manufacturing costs.